Counter track joints are described in DE 100 60 119 A1, for example. Counter track joints typically comprise an outer joint part which includes a first longitudinal axis (La), an attaching end and an aperture end which are positioned axially opposite one another, as well as first outer ball tracks and second outer ball tracks. The outer joint part works with an inner joint part which comprises a second longitudinal axis (Li) and an attaching mechanism for a shaft pointing towards the aperture end of the outer joint part, as well as first inner ball tracks and second inner ball tracks. The first outer ball tracks and the first inner ball tracks form first pairs of tracks with one another. The second outer ball tracks and the second inner ball tracks form second pairs of tracks with one another. The pairs of tracks each accommodate a torque transmitting ball. A ball cage is positioned between the outer joint part and the inner joint part and comprises circumferentially distributed cage windows which each receive at least one of the torque transmitting balls. The centers (K) of the balls are held by the cage in a central ball plane (EK). The travel of the centers (K) of the balls in the ball tracks is defined as the center line (M) of the respective ball tracks. In a longitudinal section, the tangents at the balls in the points of contact with the ball tracks form opening angles relative to one another in the ball tracks. When the joint is in the aligned condition, the opening angle (α) of the first pairs of tracks opens from the aperture end to the attaching end. When the joint is in the aligned condition, the opening angle (β) of the second pairs of tracks opens from the attaching end to the aperture end.
Neglecting for a moment the necessary play for the balls, the center lines of the first and second pairs of tracks in an aligned joint are substantially mirror-symmetrical relative to one another with reference to the central plane (EM) of the joint; and when the joint is articulated, they are mirror-symmetric relative to one another with reference to the angle-bisecting plane. The “opening angles” are the angles between tangents at a ball in its points of contact with the track base lines and, respectively, between tangents at the track base lines in points of their greatest proximity to a ball. “Control angle” refers to the spatial angles between tangential planes at a ball in their points of contact with the track flanks under torque. Both angles can change when the joint is articulated and, in a qualitative sense, follow the same course. The angle-bisecting plane of these angles determines the direction of the forces acting from the pair of tracks on to a ball.
The terms “aperture end” and “attaching end” do not exclude the possibility that the counter track joint can be designed in the form of a disc joint which includes an aperture at the attaching end, too. In all cases, the aperture end is the end pointing to the entrance of the shaft into the inner joint part. To characterise the axial directions, the terms “attaching end” and “aperture end” are also used, and remain unchanged, with reference to the inner joint part.
In counter track joints as described in DE 100 60 119 A1, the forces acting on the balls in the first and second pairs of tracks point in opposite directions. The forces are supported by the cage which is thus subjected to a resultant axial force becoming zero. In consequence, the cage is supported in the outer joint part in a way which is substantially free from axial forces, so that the joint is characterised by low friction and thus by ease of operation and a high degree of efficiency.
From DE 100 60 220 A1, there are known counter track joints wherein the first pairs of tracks whose control angles open from the aperture end to the attaching end are widened at the aperture end, taking an S-shaped course. This means that the track center lines of the first outer ball tracks of the first pairs of tracks are curved outwardly towards the aperture end and that the track center lines of the first inner ball tracks are curved outwardly towards the attaching end. This S-shaped course taken by the ball tracks permits an increased joint articulation angle because when the joint is articulated, the balls which move towards the joint aperture are moved across a larger articulation range when still in the ball tracks and are able to contribute to the transmission of torque.
It has already been mentioned in the above publication that the second pairs of tracks of counter track joints of this type can be provided with a design as known from UF (undercut-free) joints or Rzeppa joints, i.e. that the center lines of the outer ball tracks and inner ball tracks consist of circular tracks whose centers are mutually axially offset relative to the central plane of the joint, or they are composed of such circular arches with tangential straight lines adjoining same in opposite directions.
From U.S. Pat. No. 6,319,1331, it is known, even with genuine UF (undercut-free) joints or Rzeppa joints which comprise only pairs of tracks of the type mentioned last, to increase the possible angle of articulation by widening the ball tracks at the aperture end in the outer joint part, and in this case, too, it is possible to achieve a certain advantage in respect of ball guidance and torque transmission by the balls when the joint is articulated at the balls moving in the outer joint part towards the aperture.
The disadvantage of counter track joints, more particularly those wherein the track center lines of the first pairs of tracks are S-shaped, arises in the case of large articulation angles, where there occur positions in which the cage is no longer torque-balanced around the articulation axis. This leads to a deterioration in the joint control and can lead to jamming in the joint.